Insights into new bacteriophages of Lactococcus garvieae belonging to the family Podoviridae

Isolation, characterization, and genomic analysis of three novel Herelleviridae family lytic bacteriophages against uropathogenic isolates of Staphylococcus saprophyticus

BACKGROUND

Staphylococcus saprophyticus (S. saprophyticus) is the second most prevalent etiological agent of urinary tract infections (UTIs) in young women. However, there is a paucity of data regarding its bacteriophage (phage). Therefore, this study was conducted to isolate and identify new lytic phages from municipal wastewater with the objective of increasing knowledge about phages and their genomes.

METHODS

A total of 11 clinical isolates of S. saprophyticus and 30 wastewater samples were used to isolate three lytic phages (vB_SsapH-Golestan-100, vB_SsapH-Golestan101-M, and vB_SsapH-Golestan-105-M). The morphology, behavioral characteristics, and complete DNA genomes of these phages were analyzed.

RESULTS

The microscopic images of the phages revealed that the sizes of their heads and tail lengths fell within the ranges of 90-111 nm and 234-266 nm, respectively. All phages exhibited high adsorption rates (99.5% in 15 min) and burst sizes (150-210 PFU per infected cell), with a potential for a narrow host range. Genomic analysis of Staphylococcus phages indicated a size of 136,433 base pairs (bp) with a guanine-cytosine (GC) content of 33.7% and 192 open reading frames (ORFs) for vB_SsapH-Golestan-100, 144,081 bp with a GC content of 29.6% and 205 ORFs for vB_SsapH-Golestan101-M, and 142,199 bp with a GC content of 30.6% and 203 ORFs for vB_SsapH-Golestan-105-M. A bioinformatics analysis indicated that all three phages belong to the Twortvirinae subfamily of Herelleviridae. Among the three phages, vB_SsapH-Golestan-100 exhibited the least similarity to previously known phages, with less than 21% similarity with its closest counterparts in genomic databases.

CONCLUSIONS

This study identified new phages that have the ability to destroy a broad range of S. saprophyticus isolates and may potentially be classified as a new genus and species within the Herelleviridae family in future studies.

Isolation and characterization of ɸEcM-vB1 bacteriophage targeting multidrug-resistant Escherichia coli

OBJECTIVES

The aim of this study is to screen for, isolate and characterize a bacteriophage designated ɸEcM-vB1 with confirmed lytic activity against multidrug-resistant (MDR) E. coli. Methods done in this research are bacteriophage isolation, purification, titer determination, bacteriophage morphology, host range determination, bacteriophage latent period and burst size determination, genomic analysis by restriction enzymes, and bacteriophage total protein content determination.

RESULTS

ɸEcM-vB1 bacteriophage exhibited high lytic activity against different MDR E. coli isolates and showed stability over wide pH and temperature range. It belongs to the Myoviridae family of the caudovirales order according to TEM. It had a latent period of 5 min and an average burst size of 271.72 pfu/cell. Genomic analysis revealed that it is susceptible to digestion by EcoRI. Ten structural proteins were detected by SDS-PAGE. ɸEcM-vB1 is considered a promising candidate for phage therapy applications.

Isolation, Characterization and Genomic Analysis of a Novel Bacteriophage VB_EcoS-Golestan Infecting Multidrug-Resistant Escherichia coli Isolated from Urinary Tract Infection

Escherichia coli (E. coli) is one of the most common uropathogenic bacteria. The emergence of multi-drug resistance among these bacteria resulted in a worldwide public health problem which requires alternative treatment approaches such as phage therapy. In this study, phage VB_EcoS-Golestan, a member of Siphoviridae family, with high lytic ability against E. coli isolates, was isolated from wastewater. Its burst size was large and about 100 plaque-forming units/infected cell, rapid adsorption time, and high resistance to a broad range of pH and temperatures. Bioinformatics analysis of the genomic sequence suggests that VB_EcoS-Golestan is a new phage closely related to Escherichia phages in the Kagunavirus genus, Guernseyvirinae subfamily of Siphoviridae. The genome size was 44829 bp bp that encodes 78 putative ORFs, no tRNAs, 7 potential promoter sequences and 13 Rho-factor-independent terminators. No lysogenic mediated genes were detected in VB_EcoS-Golestan genome. Overall VB_EcoS-Golestan might be used as a potential treatment approach for controlling E. coli mediated urinary tract infection, however, further studies are essential to ensure its safety.

Molecular investigation of two novel bacteriophages of a facultative methylotroph, Raoultella ornithinolytica: first report of Raoultella phages

Bacteria of the genus Raoultella are known to inhabit aquatic environments and can be found in medical samples. The pathogenicity of Raoultella ornithinolytica isolates in human has become increasingly important, and several cases of infections have been reported recently. However, there are no reports of isolation of bacteriophages infecting this bacterium. In this study, two novel phages (ISF3 and ISF6) of a methylotrophic Raoultella strain were isolated from sewage. To characterize the isolated phages, morphological features, protein profiles, restriction digestion patterns, and partial genome sequences were studied. Despite morphological differences, electron microscopy revealed that both phages had an icosahedral capsid connected to a contractile tail, suggesting that ISF3 and ISF6 both belong to the family Myoviridae. Partial nucleotide sequences of the ISF3 genome showed 99% to 100% identity to DNA of Klebsiella pneumonia phages KP15, KP27 and BMBT1; however, the restriction digestion profiles of ISF3 genome digested by EcoRI and EcoRV differed from those of Klebsiella phages KP15 and KP27. A partial sequence alignment showed that ISF6 can be classified as a member of a new viral genus due to its significant differences from other previously identified phages. To the best of our knowledge, this is the first report of the isolation and characterization of the specific Raoultella phages that have potential to be used as new pharmaceuticals against R. ornithinolytica.

Complete genome sequence analysis of a lytic Shigella flexneri vB-SflS-ISF001 bacteriophage

Shigellosis is one of the most important acute enteric infections caused by different species of Shigella, such as Shigella flexneri. Despite the use of antibiotic therapy to reduce disease duration, this approach is becoming less effective due to the emergence of antibiotic resistance among Shigella spp. Bacteriophages have been introduced as an alternative for controlling shigellosis. However, the bacteriophages must be without any lysogenic or virulence factors, toxin coding, or antibiotic-resistant genes. In this study, the whole genome sequence of vB_-SflS-ISF001, a virulent Siphoviridae bacteriophage specific for Shigella flexneri, was obtained, and a comparative genomic analysis was carried out to identify its properties and safety. vB_-SflS-ISF001 genomic DNA was measured at 50,552 bp with 78 deduced open reading frames (ORFs), with 24 ORFs (30.77%) sharing similarities with proteins from the genomes of homologous phages that had been reported earlier. Genetic analysis classifies it under the genus T1virus of the subfamily Tunavirinae . Moreover, comparative genomic analysis revealed no undesirable genes in the genome of vB_-SflS-ISF001, such as antibiotic resistance, virulence, lysogeny, or toxin-coding genes. The results of this investigation indicate that vB_-SflS-ISF001 is a new species, and confirm its safety for the biocontrol of S. flexneri.

Isolation and characterization of a potentially novel Siphoviridae phage (vB_SsapS-104) with lytic activity against Staphylococcus saprophyticus isolated from urinary tract infection

Antibiotic resistance is increasing among Staphylococcus saprophyticus strains isolated from urinary tract infection. This necessitates alternative therapies. For this, a lytic phage (vB_SsapS-104) against S. saprophyticus, which formed round and clear plaques on bacterial culture plates, was isolated from hospital wastewater and characterized. Microscopy analysis showed that it had a small head (about 50 nm), tail (about 80 nm), and a collar (about 22 nm in length and 19 nm in width) indicating to be a phage within Siphoviridae family. Phage vB_SsapS-104 showed a large latency period of about 40 min, rapid adsorption rate that was significantly enhanced by MgCl₂ and CaCl₂, and high stability to a wide range of temperatures and pH values. Restriction analyses demonstrated that phage consists of a double-stranded DNA with an approximate genome size of 40 Kb. BLAST results did not show high similarity (megablast) with other previously identified phages. But, in Blastn, similarity with Staphylococcus phages was observed. Phage vB_SsapS-104 represented high anti-bacterial activity against S. saprophyticus isolates in vitro as it was able to lyse 8 of the 9 clinical isolates (%88.8) obtained from a hospital in Gorgan, Iran. It was a S. saprophyticus-specific phage because no lytic activity was observed on some other pathogenic bacteria tested. Therefore, phage vB_SsapS-104 can be considered as a specific virulent phage against of S. saprophyitcus isolated from urinary tract infection. This study provided the partial genomic characterization of S. saprophyticus phage and its application against urinary tract infection associated with S. saprophyticus. This phage also can be considered as a good candidate for a therapeutic alternative in the future.

Genomic analyses of a novel bacteriophage (VB_PmiS-Isfahan) within Siphoviridae family infecting Proteus mirabilis

Proteus mirabilis is one of the most common causes of complicated urinary tract infections (UTI), especially in catheter-associated UTIs. The increased resistance to antibiotics, among P. mirabilis isolates has led us to search for alternative antibacterial agents. In this study, genome of a lytic Proteus phage VB_PmiS-Isfahan, isolated from wastewater, and active against planktonic and biofilms of P. mirabilis, isolated from UTI, was analyzed. Accordingly, the genome was sequenced and its similarity to other phages was assessed by the Mauve and EasyFig softwares. "One Click" was used for phylogenetic tree construction. The complete genome of VB_PmiS-Isfahan was 54,836 bp, dsDNA with a G+C content of 36.09%. Nighty-one open reading frames (ORFs) was deduced, among them, 23 were considered as functional genes, based on the homology to the previously characterized proteins. The BLASTn of VB_PmiS-Isfahan showed low similarity to complete genome of Salmonella phages VB_SenS_Sasha, 9NA, and VB_SenS-Sergei. A comparison of Nucleic acid and amino acid sequence, and phylogenetic analyses indicated that the phage is novel, significantly differs, and is distant from other genera, within Siphoviridae family. No virulence-associated and antibiotic resistance genes were detected. Thus, VB_PmiS-Isfahan phage is suggested as a potential novel candidate for the treatment of diseases, caused by P. mirabilis.

Isolation and Characterization of a Lytic Bacteriophage (vB_PmiS-TH) and Its Application in Combination with Ampicillin against Planktonic and Biofilm Forms of Isolated from Urinary Tract Infection

<i>Proteus mirabilis</i> is one of the most common causes of urinary tract infection (UTI), particularly in patients undergoing long-term catheterization. Phage vB_PmiS-TH was isolated from wastewater with high lytic activity against <i>P. mirabilis</i> (TH) isolated from UTI. The phage had rapid adsorption, a large burst size (∼260 PFU per infected cell), and high stability at a wide range of temperatures and pH values. As analyzed by transmission electron microscopy, phage vB_PmiS-TH had an icosahedral head of ∼87 × 62 nm with a noncontractile tail about 137 nm in length and 11 nm in width. It belongs to the family <i>Siphoviridae</i>. Combination of the phage vB_PmiS-TH with ampicillin had a higher removal activity against planktonic cells of <i>P. mirabilis</i> (TH) than the phage or the antibiotic alone. Combination of the phage at a multiplicity of infection of 100 with a high dose of ampicillin (246 µg/mL) showed the highest biofilm removal activity after 24 h. This study demonstrates that using a combination of phage and antibiotic could be significantly more effective against planktonic and biofilm forms of <i>P. mirabilis</i> (TH).

A lytic bacteriophage of the newly emerging rainbow trout pathogen Weissella ceti

This study was conducted to isolate and characterize a bacteriophage of a newly emerging pathogen, Weissella ceti, which causes weissellosis outbreaks of intensively farmed rainbow trout worldwide. The phage appeared together with the cultured Weissella ceti during isolation of pathogen from kidney of diseased rainbow trout. The morphological, physiological, proteomic and lytic spectrum were characterized. This phage, named PWc, belonged to the family Siphoviridae and possessed an isometric head (approximately 65 nm in diameter) and a flexible, non-contractile tail of 170-180 nm in length. The latent time and burst size of PWc were approximately 25 min and 16 PFU/infected cells, respectively. The PWc was relatively stable over a wide range of temperatures and pH values and possessed a broad lytic spectrum, lysing all 36 tested W. ceti strains isolated from diseased rainbow trout in Japan. The protein profile of the phage was obtained using SDS-PAGE analysis, and the potential packaging strategy was determined based on terminase large subunit sequence analysis. This is the first study to investigate a lytic bacteriophage of a newly emerging pathogen W. ceti that causes infectious disease in rainbow trout.

A virulent phage infecting Lactococcus garvieae, with homology to Lactococcus lactis phages

A new virulent phage belonging to the Siphoviridae family and able to infect Lactococcus garvieae strains was isolated from compost soil. Phage GE1 has a prolate capsid (56 by 38 nm) and a long noncontractile tail (123 nm). It had a burst size of 139 and a latent period of 31 min. Its host range was limited to only two L. garvieae strains out of 73 tested. Phage GE1 has a double-stranded DNA genome of 24,847 bp containing 48 predicted open reading frames (ORFs). Putative functions could be assigned to only 14 ORFs, and significant matches in public databases were found for only 17 ORFs, indicating that GE1 is a novel phage and its genome contains several new viral genes and encodes several new viral proteins. Of these 17 ORFs, 16 were homologous to deduced proteins of virulent phages infecting the dairy bacterium Lactococcus lactis, including previously characterized prolate-headed phages. Comparative genome analysis confirmed the relatedness of L. garvieae phage GE1 to L. lactis phages c2 (22,172 bp) and Q54 (26,537 bp), although its genome organization was closer to that of phage c2. Phage GE1 did not infect any of the 58 L. lactis strains tested. This study suggests that phages infecting different lactococcal species may have a common ancestor.

The Plasmid Complement of the Cheese Isolate Lactococcus garvieae IPLA 31405 Revealed Adaptation to the Dairy Environment

Lactococcus garvieae is a lactic acid bacterium found in raw-milk dairy products as well as a range of aquatic and terrestrial environments. The plasmids in L. garvieae have received little attention compared to those of dairy Lactococcus lactis, in which the genes carried by these extrachromosomal elements are considered of adaptive value. The present work reports the sequencing and analysis of the plasmid complement of L. garvieae IPLA 31405, a strain isolated from a traditional, Spanish, starter-free cheese made from raw-milk. It consists of pLG9 and pLG42, of 9,124 and 42,240 nucleotides, respectively. Based on sequence and structural homology in the putative origin of replication (ori) region, pLG9 and pLG42 are predicted to replicate via a theta mechanism. Real-time, quantitative PCR showed the number of copies per chromosome equivalent of pLG9 and pLG42 to be around two and five, respectively. Sequence analysis identified eight complete open reading frames (orfs) in pLG9 and 36 in pLG42; these were organized into functional modules or cassettes containing different numbers of genes. These modules were flanked by complete or interrupted insertion sequence (IS)-like elements. Among the modules of pLG42 was a gene cluster encoding specific components of a phosphoenolpyruvate-phosphotransferase (PEP-PTS) system, including a phospho-β-galacosidase. The cluster showed a complete nucleotide identity respect to that in plasmids of L. lactis. Loss of pLG42 showed this to be involved in lactose assimilation. In the same plasmid, an operon encoding a type I restriction/modification (R/M) system was also identified. The specificity of this R/M system might be broadened by different R/M specificity subunits detected in pLG9 and in the bacterial chromosome. However, challenges of L. garvieae IPLA 31405 against L. lactis phages proved that the R/M system was not involved in phage resistance. Together, these results support the hypothesis that, as in L. lactis, pLG42 contribute towards the adaptation of L. garvieae to the dairy environment.